Laserfiche WebLink
Page 2 <br /> Diane Hinson BVSPC Project 40429.601 <br /> February 26, 1996 <br /> underground storage tanks (USTs) containing gasoline were removed from the <br /> facility. Based on evidence of leakage, the District initiated an <br /> assessment to characterize the nature and extent of the contamination. By <br /> 1993, nine monitoring wells had been installed at the site and a quarterly <br /> groundwater monitoring program had been implemented. <br /> A petroleum hydrocarbon plume, approximately 50 feet in diameter, was <br /> defined at site. A feasibility study was performed in December 1993 to <br /> determine the remedial action best suited to the site. At this point in <br /> time, passive bioremediation was not considered a suitable alternative by <br /> the regulators. An active in situ bioremediation was selected as the <br /> preferred alternative based on effectiveness, implementability, and cost. <br /> Because the selected bioremediation system required re-injection of <br /> contaminated groundwater, the Central Valley Regional Water Quality Control <br /> Board (RWQCB) required a Report of Waste Discharge (RWD) be prepared so <br /> that a re-injection permit could be issued. The RWD was submitted in <br /> September 1994 as an appendix to the Remedial Action Plan. Supplemental <br /> modeling documentation, indicating that the plume would be confined to the <br /> injection/extraction area, was submitted in April 1995. The RWQCB issued a <br /> re-injection permit for the bioremediation at the Stockton Service Center <br /> in May 1995. <br /> Passive Bioremediation <br /> Passive bioremediation relies on the existing micro-organisms to biodegrade <br /> the petroleum products and only requires monitoring to document plume <br /> attenuation. It has been shown to be effective at the edges of plumes <br /> where the oxygen concentration is sufficient to support aerobic <br /> degradation. Passive bioremediation was determined to be implementable and <br /> cost effective at the Stockton Service Center site in the Additional Site <br /> Assessment and Remedial Options Report. The effectiveness, however, was <br /> uncertain because the regulatory acceptance and adequate presence of <br /> naturally occurring bacteria was unknown. Since the Additional Site <br /> Assessment and Remedial Options Report was developed, additional knowledge <br /> has been gained regarding the aquifer characteristics, microbial <br /> population, and regulatory acceptance, that indicates that passive <br /> bioremediation is a viable alternative for the Stockton Service Center <br /> Site. <br /> The District proposes to use passive bioremediation at the Stockton Service <br /> Center site instead of the active bioremediation alternative presented in <br /> the Remedial Action Report. The passive bioremediation system will require <br /> continued groundwater monitoring to confirm that the plume is not migrating <br /> and that natural attenuation is occurring. During the June 1995 meeting <br /> with the San Joaquin County Public Health Services (SJCPHS) Environmental <br /> Health Division, the District agreed to monitor seven wells (MW-1, MW-3, <br /> MW-4, MW-5, MW-7, MW-8, and MW-9) for water levels and collect groundwater <br /> samples from MW-1, MW-8, and MW-9 for TPH and BTEX analyses and monitor for <br />